This is the 4386th most frequent Japanese word.
同月
The same month.
Here, '同月' functions as 'the same month,' referring to a specific temporal coincidence with someone's retirement.
彼が退職した同月に新しい人が採用されました。
The same month he retired, a new person was hired.
In this sentence, '同月' is used to indicate 'the corresponding month in another year,' a common reference in time-based comparisons.
昨年の同月と比較して、売上が増加しました。
Compared to the same month last year, sales have increased.
This usage of '同月' refers to a specific month shared by multiple events within the same temporal frame.